1. Field of the Invention
This invention relates to non-synchronized tissue retroperfusion at low flow rates and low pressures and more particularly, it relates to catheters for coronary sinus retroperfusion and methods of retroperfusion with such catheters.
2. Description of the Related Art
In the United States, over 1.5 million persons annually suffer from intractable ischemia or acute myocardial infarction, or both. Retroperfusion techniques for the heart generally involve the forceful delivery of arterial oxygenated or venous blood. This blood is delivered retrogradely to the endangered ischemic myocardium through its adjoining coronary veins in a direction opposite to the normal outflow of venous blood through that vein. Such retroperfused blood crosses from the coronary veins into the tissue capillary circulation, e.g., as microcirculation, to provide blood and nourishment to an underperfused myocardium.
Coronary sinus retroperfusion limits or reduces myocardial damage when administered as a preemptive or remedial treatment, or both. Coronary sinus retroperfusion also may be effective therapy when targeted to slow or, in some cases, reverse the progression from myocardial ischemia to the irreversible damage associated with myocardial infarction. Further, it may provide a temporary therapeutic window to achieve even more complete revascularization, such as by Percutaneous Transluminal Coronary Angioplasty (PTCA) or Coronary Artery By-Pass Grafting (CABG), and permits physicians to improve myocardial salvage.
A two-step surgical procedure involves creating a interventional shunt from the aorta (arterial blood) to the coronary sinus (venous circulation), and subsequently restricting the coronary sinus, such as with an occluding balloon, to facilitate effective retroperfusion of coronary veins with arterial blood. Nevertheless, this procedure may result in myocardial or vascular damage, or both. This damage may be attributed to the development of excessive congestion, edema, or hemorrhages resulting from interference with the coronary venous drainage and may cause permanent damage to the myocardium, which consequently may lead to infarction or death, or both. As a result of the difficulties encountered with such procedures and rising interest in surgical revasularization of coronary arteries as a means for treatment of coronary artery disease, research in coronary sinus retroperfusion slowed. Research involving surgical retroperfusion has explored the development of more regional coronary venous delivery of cardioplegic and other therapeutic solutions to particular zones of the heart, thus attempting to curtail potential myocardial damage due to poor coronary artery perfusion.
More recently, clinically oriented synchronized retroperfusion techniques have been used to reduce the hazards of myocardial edema mentioned above. Synchronized retroperfusion is achieved by the phasing of shunted arterial blood. Shunted arterial blood is pumped retrogradely into a coronary vein during diastole, while allowing coronary venous drainage in systole. The systolic pressure is the pressure exerted by the blood on the vessels, as a result of the force created by the contraction of the heart. This "time sharing" of the coronary veins permits a synchronized retroperfusion with unidirectional retrograde delivery of oxygenated blood into the ischemic area. Retrograde delivery is followed by normal coronary venous drainage. Such a method may support the acutely ischemic myocardium, restore its function, and reduce infarct size. The method also allows pharmacologic agents to be delivered along with oxygenated blood retroperfusion.
Coronary sinus retroperfusion methods, such as Synchronized Retroperfusion (SRP) or Pressure Controlled Intermittent Coronary Sinus Occlusion (PICSO), utilize high flow rates, such as flow rates in a range of about 100 to 250 mil./min. or pressure greater than about 30 mm Hg, or both. Such high flow rates also may result in large fluctuations in coronary sinus pressure. Large pressure fluctuations increase the risk of myocardial edema and damage from the coronary sinus intervention. In an attempt to reduce the risk of such damage, complicated gating and precise pressure monitoring are employed to control pressure fluctuations. Further, retroperfusion with arterial blood may involve at least two percutaneous catheter entries; a first entry in the artery from which blood is withdrawn and a second entry in the vein to which blood is infused. Thus, the use of coronary sinus retroperfusion generally has been limited to relatively small experimental, clinical trials because of concerns about the potential tissue damage which may be inflicted on patients if these techniques were widely used and less stringently controlled.
In synchronized retroperfusion, complex devices, such a pressure monitor devices, are attached to sensitive transducers and electronic monitoring devices capable of measuring, for example, arterial and pulmonary pressure to a high degree of accuracy. Such pressure monitor devices, however, may cause bubble formation within the artery. Such bubbles may eventually interfere with the pressure monitoring. In sophisticated pressure monitor devices, the bubbles are dislodged, and bubble gases vented. In order to effectively eliminate bubbles, it may be necessary to remove the pressure monitor device from the patient. Given the sensitivity of such devices, proper orientation is also significant. Pressure monitor devices are attached and reattached in a suitable position and level with the heart, so that movement of the device is limited in three axes.
Pressure monitor devices also are used in connection with a Swan-Gantz or pulmonary artery or arterial line catheters to assess the condition of patients in cardiovascular distress. Swan-Gantz catheters may be fed to a patient's pulmonary artery via the subclavian or jugular vein to directly monitor the pressure at one or more points. In order to obtain an accurate pressure reading, a balloon at the end of the catheter is inflated to block the artery and force back pressure, so that the catheter will only be exposed to the systolic pressure within the artery. Such pressure monitor devices may be connected to a transducer which converts the pressure signal to an electronic signal which may then be recorded on a chart monitor. A Swan-Gantz catheter and a pressure monitor device may be used, for example, to assess cardiovascular and pulmonary function, left ventricular function, and fluid status and cardiac output. These type of assessments generally are made on patients who suffer from cardiac conditions, such as left ventricle failure, cardiogenic shock, myocardial infraction (heart attack), hypovolemia (inadequate blood volume), and complex circulatory situations, such as acute burns.
Current retroperfusion catheters and retroperfusion methods present several disadvantages. The high flow rates or resultant high pressures, or both, may cause perforation and bleeding into the pericardium. PICSO and SRP occlude the coronary sinus and, therefore, raise coronary sinus pressure. For example, PICSO employs an inflatable balloon to occlude the coronary sinus, as described in U.S. Pat. No. 4,934,996 to Mohl et al. In addition to raising coronary sinus pressure by occluding the coronary sinus, SRP delivers an arterial blood flow at an increased force or flow rate. The risk of bleeding is high in SRP and PICSO methods and with surgical retroperfusion between a coronary artery and a coronary vein. Although bleeding is a danger in any tissue retroperfusion, bleeding in the pericardium is especially dangerous due to the risk of cardiac tamponade, i.e., compression of the heart's venous return due to increased volume of fluid in the pericardium. Further, because synchronized retroperfusion depends upon accurate pressure measurements to maintain safe retroperfusion, malfunctions in the pressure monitor device may cause coronary blood vessels to rupture or severe damage to the heart chambers. Moreover, the insertion of catheters at two entry points, e.g., an artery and a vein, in order to retroperfuse tissue with arterial, e.g., oxygenated, blood complicates retroperfusion and increases the invasiveness of the retroperfusion.
Such catheters are also cumbersome and may prove difficult to insert even for a trained cardiologist or cardiothoracic surgeon. The difficulty in inserting such catheters stems in part from the difficulty in accurately locating the catheter during insertion and precisely positioning the catheter's infusion port(s) within the coronary sinus, so that it does not slip out during retroperfusion. Further, because of the risk of myocardial damage caused by over-pressures, the retroperfusion flow is carefully monitored and controlled. However, as noted above, the complicated and expensive control monitor devices do not eliminate this risk. Moreover, in view of the severity of the risks involved, the very complexity of the control measures used in present retroperfusion processes may make such controls an unsuitable solution to the problems associated with high flow rate or overpressure, or both, in the general application of such methods.